One manner of generating electrical power in the form of alternating current to provide electrical power for an electrical load, especially when connection to a larger electrical power grid supported by utilities is not be readily available (i.e. “off-grid”), is to utilize a generator set, or genset for short. A genset includes in combination a prime mover and an electrical generator or alternator. The prime mover may be a mechanical engine such as an internal combustion engine (e.g., a diesel compression ignition engine) or gas turbine in which a hydrocarbon-based fuel and air is combusted to release the chemical energy therein and to convert that energy into a mechanical or motive force. The motive force, in turn, is used to rotate a rotor relative to a stator of the generator so that a magnetic field produced by one component induces electrical current in the field windings associated with the other component. The generated electricity is used to power electrical equipment, i.e., the electrical load connected with the genset via an electrical network or circuit.
The genset may output electrical power as alternating current measured in watts or kilowatts, with the quantity of power generated being determined as the product of the current produced by the electrical generator with the potential or voltage across the genset. If possible, the genset is operated below its rated capacity to avoid wasting fuel. Occasionally, however, the power demand may be larger than can be supplied by a single genset. In such instances, multiple gensets may be operated together in a parallel arrangement to jointly meet the power demand. With arrangements of multiple gensets, especially when isolated from a larger electrical grid that could dictate their operation, it is necessary to distribute the electrical load among the plurality and to synchronize their operation to match the speed and frequency with the frequency of the electrical load. One method of distributing electrical load among a plurality of gensets is symmetric load sharing, in which the load is distributed proportionally according to the rated capacity or rated output of each genset. Hence, the gensets are all being operated at the same percentage of their individual, relative capacity, and theoretically should be subjected to the same level of stress and wear, even though some gensets may be producing a larger absolute output than other gensets.
While symmetrical loading may address load distribution and synchronization with respect to the electrical characteristics of the plurality of gensets, it might not necessarily account for efficiencies and other considerations associated with the prime mover portion of the genset. For example, the prime mover, such as an internal combustion engine, may operate at peak fuel efficiency, as determined by a torque-fuel curve, that may not correlate with the output of the genset being requested by the symmetric load sharing arrangement. Other considerations that may not be accounted for include emissions from the prime mover. To address considerations associated with the prime mover, another technique for allocating the power demand among multiple gensets is asymmetric loading. An example of asymmetric loading or load sharing is described in U.S. Publication No. 2014/0152006 (“the '006 publication”) in which an efficiency database with fuel efficiency data is consulted when allocating power demand among gensets. With asymmetric load sharing, operation of the gensets may not be directly proportional and may occur with a degree of independence between gensets.
Under either the symmetrical or asymmetrical loading method, it is necessary to accommodate fluctuations or changes in the power demanded by the electrical load, which may increase or decrease as devices are switched on and off. The changes in power demand may occur rapidly and dynamically. Accounting for these changes is complicated by the fact that different gensets in the plurality may have different operating characteristics and are provided in different output capacities and sizes. The present disclosure is directed to addressing these considerations.